1. Field of the Invention
This invention generally relates to wireless communications and, more particularly, to heating and cooling radio base stations.
2. Description of the Related Art
Wireless communication has experienced explosive growth. In just a few years cellular telephone usage has soared, and growth continues as wireless Internet access improves. This explosive growth has revolutionized data and voice communication, and manufacturers are continually striving to improve wireless equipment to meet the explosive growth.
Radio base stations are one example of continuously improving wireless equipment. Radio base stations are self-contained enclosures that house transmitters, receivers, and other wireless communication equipment. While radio base stations were originally designed for indoor installations, explosive growth has forced manufacturers to design outdoor radio base stations. These outdoor radio base stations are large, so wireless service providers often seek installation sites on the roofs of buildings. Tall urban buildings provide better transmission and reception while hiding the often aesthetically-unpleasant radio base station.
These outdoor radio base stations, however, are prone to overheating. The roofs of urban buildings are very hot in the summer and very cold in the winter. If the wireless communication equipment is exposed to temperatures lying outside an operating range, the equipment may fail from thermal stress. Some radio base stations have heaters and air conditioners to keep the wireless communication equipment within the operating range. Even with air conditioning, however, light breezes can drastically affect the radio base stations. These breezes blow into the radio base station and frequently cause the wireless communication equipment to fail from overheating. When the wireless communication equipment fails, wireless service is interrupted. An interruption in service irritates customers, disrupts daily business activities, and reduces revenue for the service provider.
FIG. 1 shows the prior art problem that causes radio base stations to thermally fail. FIG. 1 is a schematic drawing of a prior art radio base station 10. The prior art radio base station 10 includes a cabinet 12 that houses wireless communication equipment (not shown for simplicity). An electric fan 14 is shown through a cutaway portion 16 in the cabinet 12. The fan 14 is a component of a heating, ventilating, and air conditioning (HVAC) system that cools the wireless communication equipment (the complete HVAC system, for simplicity, is also not shown). The fan 14 is designed to exhaust air through one or more vents 18 in a hood 20. The problem, however, is that breezes blow through the vents 18 and straight into the fan 14. These breezes, as explained below, eventually cause the wireless communication equipment to fail.
Breezes reverse spin the fan 14. Breezes flow through the hood 20 and into the fan 14. If the fan 14 is not receiving electricity, the breezes spin the fan 14 in reverse. As the fan 14 free-spins in reverse, the fan 14 draws in warm air. When the HVAC system detects rising temperatures in the prior art radio base station 10, an air conditioner turns on and sends alternating current to the fan 14. The fan 14, however, is already spinning in reverse due to the breeze. When alternating current is applied to the reverse-spinning fan 14, the fan 14 does not change direction—the fan 14 actually speeds up and continues to reverse spin. The fan 14 has a “squirrel-cage” design which permits the fan 14 to run in either direction. Although the air conditioner is operating, the fan 14 is spinning in reverse and drawing hot air into the air conditioner. The air conditioner quickly becomes ineffective, and the wireless communication equipment exceeds the maximum operating temperature. The prior art radio base station 10 then fails from thermal stress.
This prior art design creates another problem. Ambient air is contaminated with dust and dirt. The direct flow path from the vents 18 to the fan 14 carries dust and dirt into the air conditioner. The fan 14 clogs and the cooling efficiency of the air conditioner reduces. Even if the HVAC system is filtered, the filter also clogs and obstructs air flow into the HVAC system. The direct flow path from the vents 18 to the fan 14 allows dust and dirt to cascade toward thermal stress failures.
There is, accordingly, a need for a radio base station that has a reduced rate of thermal stress failures, a radio base station that is less susceptible to dust and dirt infiltration, and, yet, a radio base station design that can resolve the prior art problems without extensive tooling or revisions.